The present invention concerns a compact broadband rectangular to coaxial waveguide junction. More particularly, it concerns apparatus for transducing the TE.sub.10 mode in rectangular waveguide to the TE.sub.11 mode in a combined circular-coaxial waveguide.
A need exists for an improved means for coupling electromagnetic energy in a rectangular waveguide to a circular coaxial waveguide. It is especially needed in dual or multiband waveguide systems which utilize microwave components such as dual or multiband feeds, multiplexers and multi-channel rotary joints.
One known type of microwave waveguide transducer utilizes TEM coaxial line probes and is described in the following publications:
(1) M. L. Livingston, "Multi-frequency Coaxial Cavity Apex Feeds", Microwave Journal (October 1979) pp 51-53. PA0 (2) E. Malowicki, "Coaxial Cavity Radiator", IEEE Transactions on Antennas and Propagation (September 1969) pp 637-640. PA0 (3) A. E. Williams and F. L. Frey, "A Dual-Polarized 5-Frequency Feed", National Tele-communication Conf. (1976) pp 494-1, 494-2. PA0 (4) E. A. Ohm, "A Broad-band Microwave Circulator", IEEE Transactions on Microwave Theory and Techniques (October 1956) pp 210-217. PA0 (5) U.S. Pat. No. 3,004,228 entitled "Orthogonal Mode Transducer", issued Oct. 10, 1961 to R. L. Fogel. PA0 (6) U.S. Pat. No. 2,682,610 entitled "Selective Mode Transducer", issued June 29, 1954 to A. P. King. PA0 (7) I. R. Ravenscraft, "Primary Feeds for the Goonhilly Satellite-Communication Aerial", NASA SP-32, 4 (December 1965) pp 2141-2155. PA0 (8) A. F. Sciambi, "Five-Horn Feed Improves Monopulse Performance", Microwaves, (June 1972) pp 56-58.
The aforementioned coaxial probe devices are lossy at the higher microwave frequencies and also require tight control of mechanical tolerances in their fabrication. Therefore they are limited to applications in the lower microwave frequency bands.
Another known type of microwave transducer couples rectangular to circular waveguides through resonant irises. This concept can be conceivably extended to coaxial waveguide by adding a center conductor. Examples of iris type transducers without a center conductor are described in the following publication and patents:
Such devices using coupling irises generally require tight control of mechanical tolerances and are relatively narrow band with low power handling capacity.
Still another known type microwave transducer device for coupling rectangular to circular waveguide employs shorted metal fins with tapering thickness, such as disclosed in the following publication:
Yet another known microwave transducer device utilizes turnstyle junctions, as discussed in the following publication:
Shorted metal fin and turnstyle designs as disclosed above require rather long physical length and are expensive to fabricate.